The invention generally relates to a switching contact arrangement for a low-voltage power circuit breaker. More preferably, the switching arrangement includes the following features:
a stationary contact group including
a stationary main contact,
a stationary intermediate contact,
a stationary consumable contact, and
a stationary arcing horn,
a moving contact group, which is arranged such that it can move relative to the stationary contact group for connection and disconnection,
a contact lever, which is associated with the moving contact group and is mounted such that it can pivot against the force of a contact force spring, and having
a movable main contact,
a movable intermediate contact,
a movable consumable contact, and
a movable arcing horn,
with the capability of the contact lever to pivot during disconnection allowing the consumable contacts to open after the opening of the main contacts formed by contact facings.
Switching contact arrangements have been disclosed in DE-B 1 118 317. They are distinguished in comparison to arrangements including only one or two contact points by having a higher switching capacity, a longer life and less heating during long-term connection. They are thus used in low-voltage power circuit breakers for particularly demanding loads, and can be designed for a rated current of several thousand amperes and a switching capacity of up to 100 000 A. The disconnection process takes place in such a way that the final disconnection of the movable contact group from the stationary contact group takes place only on the consumable contacts which, in accordance with their function, are also referred to as arcing contacts or else initial contacts. The main contacts are opened first of all, so that they are not loaded, or are loaded only slightly, by switching arcs. The main contacts thus remain in a good condition over a large number of switching operations, and the current carrying capacity is maintained over a long time period, with little heating during continuous operation.
It has already been mentioned that it is desirable for the switching contact arrangement to be heated as little as possible during long-term connection and when loaded with a high continuous current. Apart from reducing the load from switching arcs on the main contacts by way of the consumable contacts, it is also known for a small amount of heating to be achieved by way of special contact facings which contain a noble metal, particularly silver, and further additives which ensure the desired mechanical hardness, as little tendency as possible to welding with an interacting contact, and resistance to corrosion. Contact facings of this type require complex production processes, and must be connected permanently, and over a large area, to their support by soldering or welding. Equipping switching contacts with contact facings of this type thus represents a considerable proportion of the costs of the switching contact arrangement for a power circuit breaker. The switching contact arrangement according to the cited DE-B 1 118 317 adopted the approach of designing all three contact points, that is to say the main contacts, intermediate contacts and consumable contacts, as suitably shaped contact facings, with the three contacts being combined in a single length, corresponding to a flat bearing plate, only on the side of the movable contact group. Thus, when connected, both the main contacts and the intermediate contacts are touching. During disconnection, the movable contact lever pivots about the intermediate contact, with the main contacts being disconnected and the consumable contacts meeting one another. As the disconnection process continues, only the consumable contacts still touch, before they are also disconnected, with a switching arc being formed.
With regard to the considerable cost contribution from contact facings in switching contact arrangements, there is a desire to restrict the number of contact points and their equipment with contact facings composed of special contact materials. Thus, for example, it is already known for only two contact points to be provided per switching contact arrangement, namely main contacts and consumable contacts, and for only the two main contacts to be designed as contact facings composed of special contact material (DE 197 27 696 A1). Combinations are also known, in such a manner that, in addition to the two main contacts, only one of the consumable contacts has a contact facing (EP 0 325 767 B1). Those contact points which have no contact facings are in this case located directly on the main bodies (which are generally composed of copper or steel) of the current path through the power circuit breaker, such as busbars, contact levers and arcing horns. The particular performance that is intrinsic with the contact arrangement according to DE-1 118 317 B described initially can thus, however, not be achieved without further effort.
Furthermore, a contact arrangement having three contact points is known (FR 1 019 187 A), during whose opening the two main contacts, which are arranged like a bridge, the intermediate contacts and the consumable contacts are disconnected successively. Only the main contacts have contact facings. In this contact arrangement, an arcing horn which forms the movable intermediate contact and the movable consumable contact is arranged such that it can pivot on the contact lever, and has the force of its own contact force spring applied to it. The contact lever is itself subject to the influence of a contact force spring, which is a component of a coupling element that connects the contact lever to an operating shaft. This contact system simplifies the pivoting arrangement of the movable arcing horn on the contact lever, ensuring the desired movement sequence with sequential disconnection of the contact points. On the other hand, the accommodation of the two contact force springs is physically more difficult, the two springs are different and, since the two springs are mechanically connected in series, problems can arise in maintaining the desired contact forces.
In this context, the invention is based on an object of providing a switching contact arrangement having triple contacts of the type mentioned initially. Preferably, the production involves considerably less effort, and the switching contact arrangement is distinguished by a longer life.
According to the invention, an object is achieved by at least one of the following further features:
the pivoting contact lever is integral and has the movable main contact, the movable intermediate contact, the movable consumable contact and the movable arcing horn,
the contact lever is itself arranged such that it can pivot on a contact support which can move about a pivoting bearing in the power circuit breaker, and the pivoting of the contact lever relative to the contact support about an associated pivoting bearing is limited by a stop,
the contact force spring is arranged between the contact support and the contact lever,
the stationary intermediate contact is formed by an end surface of a busbar to which the stationary main contact is fitted,
the stationary consumable contact is formed by an outward bulge on the stationary arcing horn which projects beyond the end surface of the busbar, on the movable arcing horn, and
the movable intermediate contact is formed by an outward bulge
the movable consumable contact is formed by a subsection of that flank of the movable arcing horn which faces the stationary arcing horn.
The advantages of a switching contact arrangement with triple contacts are in this way achieved using only one pair of contact facings, by a specific arrangement and configuration or modification of components of a switching contact arrangement in the way that they have already been used in the past. There is thus no need for any additional parts, or parts which are complex to manufacture. Nevertheless, a longer life is achieved, since the contact lever is caught during connection with its arcing horn on the stationary contact group and is largely relieved of a bending load which would otherwise occur. This allows contact levers with a relatively small cross section to be chosen, which is advantageous for the achievable switching speeds. The stop makes a contribution to achieving high switching speeds since, during connection, the pivoting angle of the contact lever after the consumable contacts touch and until the intermediate contacts touch is restricted, and the mechanical load is accordingly reduced.